1. Field of the Invention
This invention relates to a fluid-sealed anti-vibration device principally for use in an automotive engine or any other vibratory body in a vibration-proof manner.
2. Description of Related Art
A typical fluid-sealed anti-vibration device is constructed so that a first fitting to be mounted on a vibration-generator side such as an engine and a second fitting of a cylindrical form to be mounted and secured to a support side such as a vehicle frame, etc. are connected through a vibration-insulating base made of a rubber material, a diaphragm is disposed to oppose the vibration-insulating base at a lower side of the second fitting, an internal room between the vibration-insulating base and the diaphragm is made into a fluid-sealed chamber, which is in turn divided by a partition member into two chambers at the vibration-insulating base side and at the diaphragm side, both chambers being put into communication with each other through an orifice, whereby a vibration-damping function is performed owing to a liquid fluidization effect between both liquid chambers through the orifice and a vibration-insulating effect of the vibration-insulating base.
Of fluid-sealed anti-vibration devices of this type, such a device is known in the art that has a partition member constructed of an elastic membrane, as a valve member, reciprocating to displace and a pair of upper and lower grids limiting the movement of the elastic membrane. With the anti-vibration device having the elastic membrane like this, under low frequency and large amplitude vibrations such as a vibration ascribed to irregularities on the road surface when the vehicle is traveling, the fluid flows through the orifice to fluidize between the two chambers, as a result of which the device serves to exhibit a vibration-damping function. On the other hand, under high frequency and slight amplitude vibrations such as a vibration ascribed to revolution number of the engine, the above-mentioned orifice does not work, but the elastic membrane reciprocates to deform thereby exhibiting a vibration-damping function.
FR Patent Publication No. 2674590 A discloses a one wherein a partition member partitioning an upper and a lower liquid chambers is made up of a pair of upper and lower grids and an elastic membrane held between the grids. According to the patent publication, the elastic membrane is provided so that its central part may be sandwiched and held between the upper and lower grids and its peripheral portion may float, the elastic membrane being provided at least one surface thereof with bosses or protuberances opposing the grids in order to prevent the generation of impinging sound of the membrane on the grids and unwanted noise. These bosses are arranged on the surface of the elastic membrane so as to be juxtaposed equally in a ring fashion and have the function that they are pressed stepwise toward the grid and then elastically relax when the elastic membrane works.
U.S. Pat. No. 5,443,245 discloses another one, wherein the partition member comparting the upper and lower chambers is constructed of a pair of upper and lower orifice members having a grid at each central part and forming an orifice channel at each peripheral part, and an elastic membrane held between both orifice members. It further discloses the technology that with a view to preventing the generation of impinging sound of the elastic membrane on the grids and unwanted noise, the grid, not the elastic membrane, is provided with angularly adjacent, but non-repetitive non-uniform ribs wholly around the axis line.
The bosses or the ribs in the prior art technology mentioned above are thus provided to diminish the shock sound when the elastic membrane is displaced up and down to impinge on the grids, but not to limit the transfer of the sealed liquid in a circumferential direction and a radial direction among through-holes formed by the grids. In the conventional devices, therefore, transfer or leak of the sealed liquid among contiguous through-holes of the grids occurs under low frequency and large amplitude vibrations, with the result that it would be difficult to exhibit higher performance.
Again the conventional vibration-proof devices above can diminish the impinging sound or noise by means of the bosses or ribs in a sense, but the peripheral part of the elastic membrane is not restrained at all, which causes the peripheral part of the elastic membrane to flap due to a rapid change in hydraulic pressure. Hence it would be difficult to prevent necessarily sufficiently the generation of impinging sound and noise. In addition, these devices are inferior in assembling workability, as well: For instance, in assembling the partition member, the peripheral portion of the elastic membrane is liable to turn up; or when the elastic membrane will be inserted between the grids, a flat shape of the elastic membrane makes it difficult to insert.
With the above-mentioned anti-vibration device disclosed in U.S. Pat. No. 5,443,245, the orifice members of a same material are fitted in the elastic membrane thus configuring the orifice flow channel and a movable clearance of the elastic membrane. In that case, the only way to enhance the fitting precision was either to machine (cut) the fitting surface or to make a sacrifice of the dimensional precision in movable clearance of the elastic membrane. That is, the clearance dimension of the upper and lower orifice members when assembled is set by setting respective dimensions of them to be fitted and consequently, in particular where components with a large fabrication tolerance are assembled together, it was not easy to ensure the dimensional precision of the movable clearance.